Hello I'm hoping someone out there might help me find specs for the Ohm "L" crossovers. I am trying to rebuild the board from the original using modern parts. The board came with a 3way selector decibal switch that seems impossible to find today. Any suggestions would be appreciated. Thanks
Hi, I also own a pair of Ohm L speakers that I bought back in 1979. After making a few measurements I assumed a full crossover redesign was the path I would take. It is possible there are just dried out non-polar electrolytic caps in my speaker that have dropped in value and don't get the power to the tweeters anymore. I have not opened my speakers yet. I have been unable to free the woofer from the box as after removing the screws the gasket material seems to have practically glued it in there. Were you able to pull out a woofer without damage to the cabinet? Maybe I need to pull out the heat gun. I would think that the slide switch would be repairable if cleaning it with a few blasts of contact cleaner didn't work. Does your switch measure open circuit or something? Last I checked Ohm was still in business. They may be able to sell you a switch. You might also type "three position slide switch" into google and see that there are many options out there, but you will have to make measurements and find a size that works. Can you post a picture of the crossover? I'm guessing it is very simplistic . I just found a picture on AudioKarma. Yeah these are very basic.
https://audiokarma.org/forums/index...e-c2-crossovers-interesting-discovery.862724/
https://audiokarma.org/forums/index...e-c2-crossovers-interesting-discovery.862724/
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Hi Olson3 thanks for your quick reply. Starting from your first point I have to admit to doing a poor job of getting the old crossover board out as it pretty much deteriorated as I did it. I was left with the crossovers themselves just bare resistors and caps. I don't know how to measure anything as I'm newbie who's lucky I didn't destroy them. My woofers came out of the cab pretty good so I'm not sure what to tell you there. I did reach out to Ohm and they say there still in business I spoke with a fellow named Brennan and he wanted to help I believe, but he said they didn't keep spec sheets from that far back and he wasn't sure if they had replacements. I know from audio forums that the owner John has passed away recently so Im kinda leary that iIll have any luck with them. I will post pics of my CO's when I get a chance (just painted cab rear and fronts) TX
Old stuff gets brittle and can just crumble in your hands. Working at a car stereo installation garage I cut holes in the rear deck of a classic mustang for new woofers. I got out of the trunk and looked at the results. The entire vinyl covered press board deck had broken into 100 tiny pieces and dust. The senior installer laughed so hard. Anyway. Don't be in a rush and enjoy the process! The beauty of speakers is there are layers of things to learn and explore. The capacitor values are usually just printed on the side of each part. To measure capacitors and inductors I use Limp free software and my PC soundcard with a 100 ohm resistor and a few cables. If you have time to download the Arta software, read the few pages of the manual and rig up the few cables and resistor you can measure speaker impedance and determine resistor and capacitor values for the cost of the 100 ohm resistor. If you're not in a hurry that has the greatest pay off. The Arta manual is amazing. You can spend money and buy a thing called DATS from parts express that does the same thing. Or look on Amazon for a low cost DMM with capacitance and inductance settings. Here's an example LCR meter. https://www.amazon.com/Proster-Multimeter-Capacitance-Inductance-Self-discharge/dp/B07CYSV5LY/
No coil in that crossover, so it is very basic first order crossover that relies on the woofer coil inductance as the low pass filter.
A bit disappointing for what I paid for the pair I bought.
That blue capacitor in the middle of the picture says 2.2 uF on it. So you could replace it with a precision Polypropylene film cap
part like this one for just a few $. These last forever. You could go with less expensive parts of the same values too.
https://www.parts-express.com/Dayton-Audio-PMPC-2.2-2.2uF-250V-Precision-Audio-Capacitor-027-216
The other cap should have a value printed on it, but it can't be seen in the photo.
https://community.classicspeakerpages.net/topic/4631-ohm-model-l/
I saw a post that mentioned 8.2 uF for the other cap. If that is the value you have it would be replaced by this part
https://www.parts-express.com/Dayton-Audio-PMPC-8.2-8.2uF-250V-Precision-Audio-Capacitor-027-242
A bit disappointing for what I paid for the pair I bought.
That blue capacitor in the middle of the picture says 2.2 uF on it. So you could replace it with a precision Polypropylene film cap
part like this one for just a few $. These last forever. You could go with less expensive parts of the same values too.
https://www.parts-express.com/Dayton-Audio-PMPC-2.2-2.2uF-250V-Precision-Audio-Capacitor-027-216
The other cap should have a value printed on it, but it can't be seen in the photo.
https://community.classicspeakerpages.net/topic/4631-ohm-model-l/
I saw a post that mentioned 8.2 uF for the other cap. If that is the value you have it would be replaced by this part
https://www.parts-express.com/Dayton-Audio-PMPC-8.2-8.2uF-250V-Precision-Audio-Capacitor-027-242
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A hair dryer to heat the woofer frame helps soften the sticky putty holding it in. The crossover in my Ohm L is shown below. The 8.2 uF cap lower left connects to the positive input binding post not shown. With the switch in the 0 dB, top, position it is directly connected to the top tweeter in the cabinet by the blue wire upper left. The signal passes through a second capacitor, 2.2 uF and then goes to the "super" tweeter mounted just above the woofer by the green wire. The negative input binding post is connected to the switch on the right side with the white wire, so that lower switch positions form various resistor dividers to achieve he -3 dB and -6 dB attenuator ratios. The caps in my speaker measured 8.4 uF and 3.3 uF. So the 2.2 uF was actually high.
I took some measurements today and found the stock crossover cause all the problems one would expect. The woofer running without any filter breaking up and causing notch at 1 kHz, and the lower tweeter with no low pass filter messing up the upper tweeter, causing notch at 10 kHz. The -6 dB
settings on this speaker showed the best on axis response.
So I took measurements of all the drivers and used Xsim to design a basic second order three way crossover.
The results are pretty good. The Xsim software applies some smoothing. Of course a 2nd order three way cross over has way more than just
two capacitors and a few resistors in it so you can see why Ohm Acoustics never did this.
settings on this speaker showed the best on axis response.
So I took measurements of all the drivers and used Xsim to design a basic second order three way crossover.
The results are pretty good. The Xsim software applies some smoothing. Of course a 2nd order three way cross over has way more than just
two capacitors and a few resistors in it so you can see why Ohm Acoustics never did this.
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Yesterday's crossover had a lot of parts. Here's a good compromise using just a few new parts: 1.6 mH coil and 16 uF cap on the woofer and change the super tweeter capacitor from 2.2 uF down to 0.3 uF to avoid conflicting with the tweeter. The response is still a big improvement over the original
with the notch at 1kHz filled in.
The total system response is Blue. The individual drivers are S1, S4
The minimum impedance is 5 ohms just above 1 kHz.
with the notch at 1kHz filled in.
The total system response is Blue. The individual drivers are S1, S4
The minimum impedance is 5 ohms just above 1 kHz.
olsond3 made a simplified version of the crossover suggested above ( I can only be vague about the design, because when I heard the speaker in an A/B test today, the new crossover board was hidden inside the box). He said it was actually a two way, eliminating the super-tweeter and it's crossover.
I heard the original, and the olsond3 version next to each other at about 9' distance. They were both about 3'from a corner, a position that typically reinforces the bass somewhat, closer to the corner gets much stronger. Each speaker was played by itself. We played instrumental music only (Rite of Strings—Clarke, DiMeola, Ponty) in mono, but ran out of time for vocals evaluation with other favorite tracks.
For some reason, probably the inclusion of a low pass filter on the woofer, the bass was clearer when compared with the original design. Mids were clearer sounding on the new version, though the classic paper cone woofer, playing well into the mid range, had a characteristically 1970's “soft” sound, like so many other offerings from that time that had medium and large woofers crossed to tweeters, or even mids, between 1000 and 2500hz.
Bass was satisfying, and possibly a little elevated in level. The speakers did not seem boomy to me. I think that the ported alignment was well considered and executed by Ohm.
I did not notice a lack of higher treble response, but then my hearing sensitivity is already down at 10khz.
To my ears, the sound of the newly revised speaker had a much more coherent/transparent sense to it than did the original. At this point nobody has heard a revised pair in stereo.
I heard the original, and the olsond3 version next to each other at about 9' distance. They were both about 3'from a corner, a position that typically reinforces the bass somewhat, closer to the corner gets much stronger. Each speaker was played by itself. We played instrumental music only (Rite of Strings—Clarke, DiMeola, Ponty) in mono, but ran out of time for vocals evaluation with other favorite tracks.
For some reason, probably the inclusion of a low pass filter on the woofer, the bass was clearer when compared with the original design. Mids were clearer sounding on the new version, though the classic paper cone woofer, playing well into the mid range, had a characteristically 1970's “soft” sound, like so many other offerings from that time that had medium and large woofers crossed to tweeters, or even mids, between 1000 and 2500hz.
Bass was satisfying, and possibly a little elevated in level. The speakers did not seem boomy to me. I think that the ported alignment was well considered and executed by Ohm.
I did not notice a lack of higher treble response, but then my hearing sensitivity is already down at 10khz.
To my ears, the sound of the newly revised speaker had a much more coherent/transparent sense to it than did the original. At this point nobody has heard a revised pair in stereo.